Biological, physical and nutrient gradients in near-stream hydrologic
margins of hot and cold deserts
L. H. Zeglin1*, C. D. Takacs-Vesbach1, C. N. Dahm1, J. E. Barrett2, and M. N. Gooseff3
1Department
of Biology, University of New Mexico, Albuquerque, NM USA 87131
2 Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24601
3Department of Geology and Geological Engineering, Colorado School of Mines, Golden, CO USA 80401
2
Near-stream nutrient transfer is of great importance to stream and terrestrial biota. The desert stream "hydrologic margin" (HM) is a gradient of
water content and solute distribution between aquatic and terrestrial zones. A ribbon of soil where the primary limiter, water, is present, the HM is
a hotspot of biological activity and nutrient transformation.
1
Sampling schematic. Please note: A-B-C-D notation
of transect position is used for orientation of samples
and results throughout the poster.
We expect distribution of nutrients and bacterial communities to be driven by hydrologic processes, i.e. water availability across the gradient, at
both sites. Differences between sites will be related to the difference in temperature and climate.
1b
1a
Sites. Rio Salado, SEV (1); Upper and Lower Onyx River, MCM (2, 3).
See below for more information.
1c
1d
cm 0-3 3-6
SITE
E
.
c
o
li
6-10
A
B
C
3
D
H2O (g / g
Temp (C)
soil)
Rio Salado
27.7 a
Upper Onyx
Lower Onyx
0.16 a
pH
Specific
stream stream stream
NO3-N (ug / NH4-N (ug /
conductivity
NO3-N NH4-N DOC
g soil)
g soil)
(uS)
(ug/L)* (ug/L)* (mg/L)*
7.4 a
786 a
0.39 a
0.93 a
3.8
3.6
2.12
1.3 c
0.12 ab 7.7 b
12 b
0.04 b
0.04 b
14
4.1
0.435
6.5 b
0.08 b
20 b
0.37 a
0.11 b
24
4.1
0.54
7.9 b
HM
Mean values for physical parameters in 2004 samples. Conductivity at Rio Salado is +10X than
Onyx River. Extractable N and temperature values also range over an order of magnitude.
*mean values from long-term data (MCM, http://www.mcmlter.org) and July 2004 (SEV).
Figures 1a-d. Rio Salado, NM, USA. Image (1a) with visible HM; physical (1b) and nutrient (1c) gradient structure, ±1 SD;
(1d) DGGE profile of bacterial community composition (near surface water sample at left, three depths per position)
2c
2b
2a
2d
cm
0-3
E
.
c
o
li
3-6
6-10
4a
(a) Proportion of nearestneighbor 16S rRNA sequences
to clone libraries by habitat
type. Rio Salado bacteria are
more often related to
halotolerant or halophillic
organisms (e.g. Rheinheimeria
sp., Idiomarina sp.).
HM
A
B
C
D
Figures 2a-d. Upper Onyx River, Wright Valley, Antarctica. Image (2a) with visible HM; physical (2b) and nutrient (2c) gradient structure,
±1 SD; (2d) DGGE profile of bacterial community composition (near surface water sample at left, three depths per position)
3a
3c
3b
3d
cm
0-3
3-6
A
E
.
c
o
li
6-10
B
C
4b
D
HM
Figures 3a-d. Lower Onyx River, Wright Valley, Antarctica. Image (3a) with visible HM; physical (3b) and nutrient (3c) gradient structure,
±1 SD; (3d) DGGE profile of bacterial community composition (near surface water sample at left, three depths per position)
CORRELATIONS
Rio Salado
Upper Onyx
Lower Onyx
sample
(DGGE bands)
distance conductivity
water content conductivity
NO3-N conductivity
0.583 *
0.583 *
0.503 *
gradient
(DGGE bands)
site
-0.533 *
-0.473
-0.305
(DGGE bands)
Rio Salado
12
0.04
17
a
a
5
Upper Onyx
15
Lower Onyx
ab
0.12
b
22
19
0.18
b
ab
27
Chao
0.513 *
0.505 *
0.509 *
(97% sequence
similarity)
145
286
188
(Table displays alpha, beta and gamma richness metrics from DGGE, with subscripts denoting ANOVA groupings.
(Table displays Pearson’s r, * denotes a significant relationship)
Figure 5 displays 16S rRNA clone library rarefaction curves representative of each site: all curves are statistically
- All sites show a distance-conductivity and nitrate-conductivity
similar)
relationship, evapoconcentration of solutes is likely a gradient- According to DGGE, the Lower Onyx bacterial community is the most species rich and has the highest
forming mechanism in desert stream margins and nitrate
heterogeneity across the gradient, and the Rio Salado is the least species rich and most homogeneous. This is
availability appears to be controlled by this abiotic process.
suggests that biological processes (faster growth/adaptation/response to disturbance) structure bacterial
Ammonium might be best indicator of biological N cycling here.
distribution in the hot desert.
- Nitrate and ammonium are not consistently related, but total
- 16S rRNA clone library data show that: (1, Figure 5) all sites are highly diverse. Though no rarefaction curves
DIN is correlated with DGGE richness across all sites (r = 0.898, p
near a saturation point at the “species” level of sequence similarity, Rio Salado curves begin to diverge toward
= 0.000). Does higher nutrient availability allow higher diversity?
lower diversity (more sequences are being processed to resolve this pattern). (2, Figure 4) community
How does biotic activity affect nutrient distributions?
composition differs between all libraries, and suggests selection for halotolerance at Rio Salado.
Many thanks to:
METHODS
Raytheon Polar Services and Petroleum Helicopters, Inc. for logistical support in Antarctica.
The McMurdo and Sevilleta Long-Term Ecological Research programs and personnel. The
UNM Hydrogeoecology Group, especially John Craig. Field assistance from D. Bradley Bate,
Chelsea Crenshaw, Kenneth Hill and Melissa Northcott. Laboratory assistance from Nathan
Daves-Brody, Nick Enquist, Kendra Mitchell, Kris Mossberg and Erin Saulsberry-Abens.
Funding provided by the National Science Foundation OPP-#0338267 and PDF grants.
DIN is reported as the sediment KCl-extractable fraction.
Environmental genomic DNA was extracted using a MoBio PowerSoil extraction kit.
DGGEs were run with 3x replication on a 30%-70% gradient with PCR product of
338FGC and 519R 16S bacterial rRNA primers and E. coli standards.
Clone libraries are prepared with 8F and 1492R 16S bacterial rRNA primers,
composition reported as nearest BLAST hit to sequence, aligned with GreenGenes1,
statistics run on distance matrices from ARB using DOTUR2 and WebLibshuff3.
*Please direct questions and comments to Lydia H. Zeglin, lzeglin@unm.edu.
SUMMARY
Upper Onyx Lower Onyx
Nitrate gradients are related to evapoconcentration.
Total DIN is related to bacterial richness. Ammonium
is important to biotic communities, but processes
affecting its distribution are more complex.
Bacterial communities are potentially less diverse,
and certainly different in composition, at Rio Salado,
the hot site. This is likely related to site differences in
hydrologic variability: over long time scales (salinity)
and/or short (precipitation/flood regime). Gradient
structure can shift temporally (see right).
Underway: completion of clone libraries. Next:
quanitfication of functional genes (e.g. those coding
nitrogenase and ammonia monoxygenase enzymes)
across the gradients to understand bacterial
metabolic capability, and relate function to aquatic terrestrial nutrient distribution. Abiotic processes are
similar at both sites; are biotic processes, also?
E
.
c
o
li
Dec. 2005
RICHNESS
(b) Proportion of nearestneighbor 16S rRNA sequences
to clone libraries by taxonomic
group. Rio Salado bacteria are
more often related to members
of the Gamma - Proteobacteria,
while Upper Onyx River
bacteria are more often related
to members of the
Gemmatimonadetes. ALL
libraries are compositionally
different from one another (p <
0.01, WebLibshuff)
A BC D
A BC D
E
.
c
o
li
Jan. 2006
Patterns of nutrient distribution
Patterns of diversity
Figure 4.
Upper Onyx Lower Onyx
REFERENCES
1
DeSantis, T. Z., P. Hugenholtz, K. Keller, E. L. Brodie, N. Larsen, Y. M. Piceno, R. Phan, and G. L. Andersen. 2006.
NAST: a multiple sequence alignment server for comparative analysis of 16S rRNA genes. Nucleic Acids Res 34:
W394-9.
2
Schloss, P. D. and Handelsman, J. 2005. Introducing DOTUR, a computer program for defining operational
taxonomic units and estimating species richness. Appl Environ Microb. 71 (3): 1501-1506.
3
Henriksen, James R. 2004. webLIBSHUFF (http://libshuff.mib.uga.edu)
Antarctic Hydrologic Margin Project: http://www.mines.edu/%7Emgooseff/web_antarctica/antarctic_proj.html